For the past 20 years, the law enforcement community has been searching for a projectile or missile that is non-lethal, for use in circumstances that do not require lethal force. A number of devices have been developed for this purpose but only a few have been sufficiently successful to be accepted by that community. Some of these devices use a shotgun-size or larger caliber dedicated launcher, to project a solid, soft projectile; others use a smaller caliber launcher with variations of the rubber bullet concept, to inject a tranquilizer drug or just stun the target person. Other methods used include fire hoses, water cannon, mace, pepper spray and a variety of electric shock inducers. The most common devices are the tear-gas grenade and the stun-grenade. These grenades are used in riot and multiple assailant situations, not usually in one-on-one situations, which are the most common confrontations.
The mechanism used in propellant actuated devices utilizes the momentum of the projectile to stun or knock down the target person. The dispersal of a marking substance at impact is a generic benefit that allows for subsequent identification and arrest of the subject law violator.
A projectile of relatively small mass, but with large surface area (like a basketball), when launched with sufficient velocity, and impacting the target at a short range, can produce the knock down effect. The impact force is distributed over a relatively large area, thus reducing damage to the target person. If the size of the projectile is reduced to that of a baseball, (and the mass reduced proportionally) the velocity required to produce the knockdown effect is reduced, but the impact is distributed over a smaller area, increasing the potential for more local damage to the target person. If the size of the projectile is reduced to that of a ball bearing, with a proportional mass, even at relatively small velocities it can penetrate the target, and at conventional gun velocities, it becomes a lethal bullet.
An ideal low-lethality projectile would balance the area of impact, the mass of the projectile and the velocity at impact, in order to produce the desired stunning and knockdown effects, without penetrating or causing major damage to the target.